Cathodic electrocoating binders

ABSTRACT

Binders useful for cathodic electrocoating are water-dilutable on addition of acid and comprise a mixture of 
     (A) a polyadduct which carries basic nitrogen groups and contains groups of the formula (I) and/or (II) ##STR1##  where R 1  and R 2  are hydrogen or methyl and R 3  and R 4  are alkyl or hydroxyalkyl or together are a 5- or 6-membered ring, and 
     (B) a reaction product of a polyisocyanate and an olefinically unsaturated amine which carries a secondary amino group and a methacrylamide or methacrylate group.

The present invention relates to cathodic electrocoating binders basedon a mixture of a polyadduct which contains basic nitrogen groups and ablocked polyisocyanate.

Polyadducts which carry basic nitrogen groups and contain groupings ofthe formula (I) and/or (II) ##STR2## where R¹ and R² are identical ordifferent and each is hydrogen or methyl, and R³ and R⁴ are identical ordifferent and each is alkyl or hydroxyalkyl or R³ and R⁴ together are a5- or 6-membered ring, can be prepared, for example, as described inGerman Laid-Open Application DOS No. 2,942,488 and DOS No. 3,021,300.These products can be used as cathodic electrocoating binders and have anumber of very good properties, such as high stability of the coatingbaths in which they are used, a good anti-corrosion action, greatthrowing power and low baking losses.

When used in finishes, these products are advantageously hardened atabout 180° C., but if hardening catalysts, such as manganese salts orcobalt salts, are added, they crosslink at as low a baking temperatureas 170° C. to give hard and resilient films. It is an object of thepresent invention to lower the baking temperature even more and hence torealize a further saving in energy. It is a further object to make thepaint films even more resilient.

We have found that these objects are achieved by using binders whichadditionally contain a reaction product of a polyisocyanate and anunsaturated amine.

Accordingly, the present invention relates to a binder which iswater-dilutable on addition of acid, is suitable for preparing cathodicelectrocoating compositions and comprises a mixture of

(A) from 60 to 95% by weight of a polyadduct which carries basicnitrogen groups and contains groupings of the formula (I) and/or (II)##STR3## where R¹ and R² are identical or different and each is hydrogenor methyl, and R³ and R⁴ are identical or different and each is alkyl of1 to 9 carbon atoms or hydroxyalkyl of 2 to 10 carbon atoms, or R³ andR⁴ together are a 5- or 6-membered ring and

(B) from 5 to 40% by weight of a reaction product of a polyisocyanateand an olefinically unsaturated amine which carries a secondary aminogroup and a methacrylamide or methacrylate group.

The present invention also relates to the use of this binder in aprotonated form for cathodic electrocoating.

The components from which the binder is prepared will now be describedin detail.

Products described in German Laid-Open Application DOS No. 2,934,467 canbe used as the polyadduct (A) carrying basic nitrogen groups. They canbe prepared, for example, by first reacting a polymeric polyol withN-alkoxymethyl(meth)acrylamide and then forming an adduct of theresulting unsaturated polymer with a primary or secondary amine. Sincethe α,β-unsaturated amide groups in these products are bonded to thepolymer molecule via methyl ether bridges, these materials are not veryresistant to hydrolysis.

Component (A) is preferably a product as described in German Laid-OpenApplication DOS No. 2,942,488, i.e. a polyadduct which carries basicnitrogen groups, has an average molecular weight of from 500 to 10,000,and contains groups of the formula (I) bonded to aromatic rings.Polyadducts of this type can be prepared, for example, as described inGerman Laid-Open Application DOS No. 2,942,488, from monophenols and/orpolyphenols which carry groups of the formula (I), polyepoxides andamines or amine salts.

Further products preferred for use as component (A) can be prepared inaccordance with German Laid-Open Application DOS No. 3,021,300, i.e. bytaking

(a) a monophenol and/or polyphenol which carries groups of the formula(I) ##STR4## where R¹ and R² are identical or different and each ishydrogen or methyl, and forming an adduct with

(b) an amine having one or more primary and/or secondary amino groups,and reacting the product with

(c) an epoxy compound having from 1 to 4 epoxide groups per molecule anda molecular weight of not more than 2,500, and using the components (a)and (c) in amounts which are such that the ratio of the phenolichydroxyl groups of (a) to epoxide groups of (c) is from 1:0.5 to 1:2,and using the amine (b) in an amount which is such that the resultingpolyadduct of (a), (b) and (c) contains from 0.1 to 5% by weight ofbasic nitrogen.

Component (A) is present in the binder mixture according to theinvention in an amount of from 60 to 95, preferably from 65 to 85, % byweight.

According to the invention, component (B) is a reaction product of apolyisocyanate and an olefinically unsaturated amine which carries asecondary amino group and a methacrylamide or methacrylate group. GermanLaid-Open Application DOS No. 2,752,255 discloses reaction products ofdiisocyanates and/or triisocyanates with hydroxyethyl (meth)acrylate orhydroxypropyl (meth)acrylate. However, these products have littleactivity when used as crosslinking agents, so that baking temperaturesof about 180° C. are used.

The use of component (B) according to the invention, however, makes itpossible to produce fully hardened paint films without difficulty at160° C. or, if hardening catalysts, such as manganese salts or cobaltsalts, are used, even at as low a temperature as 140° C.

Component (B) can be prepared from any desired aliphatic, alicyclicand/or aromatic polyisocyanate. Examples of suitable polyisocyanates arediisocyanates, such as hexamethylene diisocyanate, isophoronediisocyanate, cyclohexane 1, 4-diisocyanate, toluylene diisocyanate anddiphenylmethane 4,4'-diisocyanate, triisocyanates, such as biuretized orisocyanurated hexamethylene diisocyanate, and the adduct formed from 3moles of toluylene diisocyanate with 1 mole of trimethylolpropane. Evenisocyanate prepolymers, for example adducts formed from diisocyanateswith polyester polyols or polyether polyols, can be used aspolyisocyanates. Especially suitable olefinically unsaturated amineswhich carry a secondary amino group and a methacrylamide or methacrylategroup are those of the formula (III) ##STR5## where R⁴ is a hydrocarbonradical of 3 to 10 carbon atoms, which has one or more branchings on thecarbon adjacent to the NH group, R⁵ is an ethylene or propylene chain, Xis oxygen or an NH bridge, and R⁴ can be, for example, isopropyl,tert.-butyl, isoamyl or ethylhexyl and preferably is isopropyl ortert.-butyl.

An example of a particularly suitable olefinically unsaturated amine isisopropylaminopropylmethacrylamide.

To prepare component (B), either the amine can be added to the amine.The reaction even proceeds at room temperature, but it can be speeded upby heating the mixture to about 150° C., preferably to about 100° C. Ifthe starting materials and the reaction product are liquid at thereaction temperature, it is possible to carry out the reaction in theabsence of a solvent, but in general the reaction will be carried out inan inert solvent, such as an ether, ester, ketone or hydrocarbon.

Component (B) is present in the binder mixture according to theinvention in an amount of from 5 to 40, preferably from 15 to 35, % byweight.

Components (A) and (B) are dissolved in organic solvents, and thesolutions are carefully mixed with each other, if appropriate atelevated temperatures. Then, possibly after the resin mixture has beenmilled together with pigments and auxiliaries, an acid, for example acarboxylic acid, such as formic acid, acetic acid or lactic acid, isstirred into the mixture to neutralize some or all of the basic groups,and the batch is then brought to the use concentration by diluting itwith water. However, it is also possible to stir the unneutralizedmaterial into water to which acid has been added.

The binders according to the invention are preferably used as paintbinders in the cathodic electrocoating of electrically conductivesurfaces, for example on metal components, sheet or the like of brass,copper or aluminum metallized plastics or materials which have beencoated with conductive carbon, and iron and steel which may have beenchemically pretreated, for example phosphatized.

A cathodic electrocoating bath is generally made up with a solidscontent of from 5 to 30% by weight. The deposition process customarilytakes place at 15°-40° C. in the course of from 1 to 5 minutes, at pH4.0-8.5, preferably pH 5.5-8.0, and at a deposition voltage of from 50to 500 volt. The electrically conductive body to be coated is connectedas the cathode. The deposited film can be hardened above 140° C. in thecourse of about 20 minutes. If the electrocoating bath does not containa hardening catalyst, it is advisable to harden at from about 160° C. to180° C. The hardening catalyst can be added either to the organicsolution of the resin or to the aqueous bath if the hardening catalystis a water-soluble salt. Suitable hardening catalysts are heavy metalsalts, e.g. salts of manganese or cobalt, although lead salts,especially if combined with one of the above metal salts, also have anaccelerating action on the hardening process and thus enable the bakingtemperature to be lowered. The catalysts are advantageously used inamounts of from 5 to 1,000 ppm of metal, based on aqueous electrocoatingbath.

The Examples illustrate the invention without limiting its scope. Partsand percentages are by weight, unless indicated otherwise.

EXAMPLE 1 Component A₁

63 parts of paraformaldehyde and 1 part of copper powder are added to940 parts of phenol and 2,020 parts of methylolacrylamide. The mixtureis dissolved by heating to 100° C., and is then cooled down to 55° C.,and 10 parts of boron trifluoride diethyl etherate are added. After 1hour at 55°-60° C., the same amount of catalyst is added once more, andthe mixture is held at 60° C. for 3 hours. It is then heated to 115° C.and held at this temperature for 30 minutes, during which about 200parts of water are distilled off. The mixture is then cooled down to 80°C. and is diluted with 1,200 parts of ethylene glycol. An amine adductis prepared therefrom by adding 500 parts of diethanolamine and 2 partsof 2,6-di-tert.-butyl-p-cresol to 1,311 parts of this solution andheating at 90° C. for 2 hours.

In a separate vessel, 580 parts of fatty acid dimer with a trimercontent of less than 4% and 210 parts of 2,2'-aminoethoxyethanol areheated to 200° C. in the course of 2 hours, during which the waterformed is distilled off, and are held at this temperature for 6 hours.The resulting product, a diamidediol, has a residual acid number of 2.3mg of KOH/g.

740 parts of a diglycidyl ether of bisphenol A with an epoxideequivalent weight of 500 are dissolved in 65 parts of hot xylene, 279parts of the above diamidediol are added, and the mixture is heated to130° C. 1.5 parts of dimethylbenzylamine are then added. The mixture isheld at 130° C. until the epoxide equivalent weight of the resultingchain-lengthened epoxy resin has risen to 1,000. 431 parts of the aboveamine adduct and 15 parts of methyldiethanolamine are added. The mixtureis then diluted with 211 parts of isobutanol and 211 parts ofisopropanol to a 70% solids content and is stirred at 70° C. After 15-20hours, the product has reached the desired viscosity of 1,000 mPa.s,measured at 75° C. in a disc cone viscometer.

Component B₁

566 parts of isopropylaminopropylmethacrylamide, 570 parts of dioxane,0.3 part of hydroquinone monomethyl ether and 0.3 part of dibutyl-tindilaurate are heated to 90° C. in a sealed nitrogen-flushed vessel. 573parts of isocyanurated hexamethylene diisocyanate having an NCO contentof 22% and dissolved in 560 parts of dioxane are then added dropwise inthe course of 2 hours, and the mixture is held at 90° C. for a further 2hours, during which the isocyanate content decreases to 0. The producthas a solids content of 50%.

Preparation of the binder

680 parts of component B₁ are added to 1,950 parts of component A₁, andthe two components are carefully mixed. 33 parts of acetic acid are thanadded.

EXAMPLE 2 Component A₂

0.1 part of copper powder is added to 188 parts of phenol, 213 parts ofacrylamide and 99 parts of paraformaldehyde, and the mixture is slowlyheated. When 80° C. is reached, the mass has substantially liquefied. Itis heated to 115° C. and is held at this temperature for 10 minutes,during which it becomes completely clear. It is cooled down to 55°-60°C., and 2 parts of boron trifluoride diethyl etherate are added. Thetemperature is held at 60° C., initially by cooling. After 1 hour, afurther 2 parts of boron trifluoride diethyl etherate are added. Themixture is held at 60° C. for a further 3 hours and is then diluted with292 parts of isobutanol. The temperature is raised to the boiling point,and about 50 parts of water are taken off in the course of 90 minutes.The product thus obtained has a solids content of 70%.

An amine adduct is prepared from the product by adding 43 parts ofdiethanolamine and 0.2 part of hydroquinone monomethyl ether to 120parts of the solution and heating the mixture at 95° C. for 2 hours.

In a separate vessel, 564 parts of an epoxy resin based on bisphenol Aand having an epoxide equivalent weight of 190, 137 parts of bisphenol Aand 247.5 parts of a polycaprolactonediol having an average molecularweight of 550, and 260.5 parts of xylene are refluxed, and watercontained in the mixture is separated off. 200 parts of xylene are thentaken off under reduced pressure. 1.25 parts of dimethylbenzylamine areadded at 150° C., and the mixture is held at 160° C. for 1 hour. It isthen cooled down to 130° C., a further 1.9 parts of dimethylbenzylamineare added, and the mixture is held at 130° C. until the epoxide valuehas dropped to 0.11 epoxide group/100 g, which takes 2-4 hours.

109 parts of the above amine adduct and 2.15 parts ofdimethylethanolamine are added to 300 parts of the above mixture. 56.6parts of isopropanol and 56.6 parts of isobutanol are added to bring thesolids content to 70%, and the mixture is heated at 70° C. After 20hours the product has a viscosity of 900 to 1,100 mPa.s, measured at 75°C. Its amine number is 45.3 mg of KOH/g of solid resin.

Component B₂

86 parts of isopropylaminopropylmethacrylamide, 83.3 parts of dioxane,0.05 part of hydroquinone monomethyl ether and 0.1 part of dibutyl-tindilaurate are heated to 70° C. in a sealed nitrogen-flushed vessel. 121parts of an isocyanate prepolymer prepared from 1 mole oftrimethylolpropane and 3 moles of toluylene diisocyanate having anisocyanate content of 17.3%, dissolved in 40 parts of ethyl acetate and83 parts of dioxane are then added dropwise in the course of 1 hour.After a further hour the isocyanate content has decreased to 0.

Preparation of the binder

183 parts of component B₂ are added to 520 parts of component A₂, andthe two components are carefully mixed. Addition of 8 parts of glacialacetic acid makes the product water-dispersible.

EXAMPLE 3 Component A₃

An amide-amine is first prepared from 290 parts of linoleic acid and 104parts of aminoethylethanolamine. For this purpose, the components areheated to 200° C. in the course of 1 hour.

The mixture is then held at 200° C. for 31/2 hours. A total of 18 partsof water are distilled off. On cooling down the product solidifies intoa waxy mass and has a basic nitrogen content of 3.5%, of which 3.3% isin the form of secondary amine and 0.2% in the form of primary amine.

600 parts of phenol, 485 parts of bisphenol A, 1,000 parts ofacrylamide, 490 parts of paraformaldehyde and 1 part of2,6-di-tert.-butyl-p-cresol are introduced in succession into a stirredvessel and are heated with stirring at 120° C. until a clear solutionhas formed. The solution is cooled down to 50° C., and 10 parts of borontrifluoride dimethyl etherate are added. The temperature is held at 50°C. by cooling, until the reaction has died down. The mixture is thenheated to 100° C. and held at this temperature for 30 minutes, duringwhich the water formed in the reaction is distilled off under reducedpressure. The product left behind is then diluted with 1,000 parts ofisobutanol to a solids content of 70%.

40 parts of the above amide-amine, 40 parts of diethanolamine and 0.1part of 2,6-di-tert.-butyl-p-cresol are added to 157.5 parts of thisproduct, and the mixture is heated at 80° C. for 1 hour. 120 parts of anepoxy resin based on bisphenol A and epichlorohydrin and having anepoxide equivalent weight of 190 (for example ®Epikote 828) and 93 partsof isopropanol are then added and the mixture is heated at 85° C. for 15hours.

Component B₃

566 parts of isopropylaminopropylmethacrylamide, 475 parts of dioxane,0.3 part of hydroquinone monomethyl ether and 0.3 part of dibutyl-tindilaurate are heated to 100° C. in a sealed vessel. A mixture of 576parts of biuretized hexamethylene diisocyanate (for example ®Desmodur Nfrom Bayer AG) with an isocyanate content of 21.9%, 81 parts of xylene,81 parts of ethylene glycol acetate and 475 parts of dioxane are thenadded dropwise in the course of 2 hours and the mixture is held at thistemperature for 1 hour, during which the isocyanate content decreases to0.

Preparation of the binder

158 parts of component B₃ are added to 450 parts of component A₃, andthe two components are carefully mixed. Addition of 12 parts of aceticacid makes the product water-dilutable.

EXAMPLE 4 Preparation of the binder

183 parts of component B₃ are added to 520 parts of component A₂, andthe two components are carefully mixed. 8 parts of glacial acetic acidare then added.

COMPARATIVE EXAMPLE

Instead of component (B), an unsaturated triurethane is prepared asdescribed in German Laid-Open Application DOS No. 2,752,255. The methodof preparation is the same as that for component B₃, except that 390parts of hydroxyethyl methacrylate are used in place of 566 parts ofisopropylaminopropylmethacrylamide, and the amount of dioxane used isonly 299 parts instead of 475 parts.

Preparation of the binder

134 parts of the above triurethane are added to 520 parts of componentA₂, and the two components are carefully mixed. 8 parts of glacialacetic acid are then added.

Testing the binders

In each case, 308 parts of binder solution are diluted with 692 parts offully demineralized water to a solids content of 20%, 40 parts ofkaolin, 6 parts of basic lead silicate pigment and 4 parts of carbonblack are added, followed by grinding medium, and the mixture isball-milled for 24 hours. The grinding medium is then separated off. 666parts of fully demineralized water are added to adjust the solidscontent in the bath to 15%. The baths are stirred at 30° C. for 48hours. Paint films are deposited at the voltage shown in the followingTable in the course of 2 minutes onto zinc-phosphatized steel testpanels connected as the cathode, and are baked at 180° C., at 160° C.and at 140° C. for 20 minutes. Thereafter the baked films are tested forresistance to acetone by rubbing them backwards and forwards 50 timeswith an acetone-impregnated cottonwool pad, and the resilience isexamined in the form of a reverse impact test. The following Table showsthe results:

    __________________________________________________________________________    Result of binder test; 17 μm film thickness                                         Ford throwing power                                                           with a 17μ  outside                                                                   Acetone resistance                                                                        Reverse impact in x lb                        Binder pH                                                                              film thickness                                                                           180° C.                                                                    160° C.                                                                    140° C.                                                                    180° C.                                                                    160° C.                                                                    140° C.                        __________________________________________________________________________    Example 1                                                                            6.7                                                                             17 cm (270 V)                                                                            1   1   3   160 160 40                                                         1*  1*  1*  160*                                                                              160*                                                                             120*                                  Example 2                                                                            6.6                                                                             16 cm (260 V)                                                                            1   1   2   160 160 40                                                         1*  1*  1*  160*                                                                              160*                                                                             160*                                  Example 3                                                                            6.2                                                                             18 cm (320 V)                                                                            1   1   3    80  40 20                                                         1*  1*  2*  160*                                                                              160*                                                                              60*                                  Example 4                                                                            6.6                                                                             15.5 cm (250 V)                                                                          1   1   2   160 160 40                                                         1*  1*  1*  160*                                                                              160*                                                                             120*                                  Comparative                                                                          6.5                                                                             15 cm (250 V)                                                                            1   5   6    40 <20 <20                                   Example              1*  3* 6    160*                                                                              40 <20                                   __________________________________________________________________________     *Baths contain 50 ppm of manganese in the form of manganese acetate           Acetone resistance: 1 = very good, 6 = inadequate                        

We claim:
 1. A binder which is water-dilutable on addition of acid, issuitable for preparing cathodic electrocoating compositions andcomprises a mixture of(A) from 60 to 95% by weight of a polyadduct whichcarries basic nitrogen groups and contains groupings of the formula (I)or (II) or (I) and (II) ##STR6## where R¹ and R² are identical ordifferent and each is hydrogen or methyl, and R³ and R⁴ are identical ofdifferent and each is alkyl of 1 to 9 carbon atoms or hydroxyalkyl of 2to 10 carbon atoms, or R³ and R⁴ together are a 5- or 6-membered ringand (B) from 5 to 40% by weight of a reaction product of apolyisocyanate and an olefinically unsaturated amine which carries asecondary amino group and a methacrylamide or methacrylate group.
 2. Thebinder of claim 1, wherein a reaction product of a polyisocyanate andisopropylaminopropylmethacrylamide is used as component (B).
 3. Thebinder of claim 1 or 2, wherein a polyadduct in which the groups of theformulae (I) or (II) or (I) and (II) are bonded to aromatic rings isused as component (A).